The invention relates generally to propshaft housings for marine engines, and more particularly, to preventing relative motion between the propshaft housing and an engine gear case.
Known outboard engines include a drive shaft which extends from the engine power head, through an exhaust case, and into an engine lower unit. The lower unit includes a gear case, and a propeller shaft extends through the gear case. A pinion gear affixed to the lower end of the drive shaft meshes with and drives two gears diametrically opposed to each other and rotationally aligned with the propeller shaft. A clutching member, which is slidingly connected to the propeller shaft, selectively engages one of the drive gears, thereby driving the propeller shaft in the same rotational direction as the engaged gear. One propeller shaft rotational direction provides forward thrust, and the other rotational direction provides reverse thrust. The rotational axis of the propeller shaft is generally perpendicular to the rotational axis of the drive shaft.
A bearing housing, sometimes referred to as a propeller shaft housing or a propshaft housing, is located within the gear case, and the propeller shaft extends through a longitudinal bore in the propshaft housing. Bearings are supported within the propshaft housing bore, and the propeller shaft rotates relative to the propshaft housing on the bearings.
Due to the significant vibrations and power transmitted by the propeller shaft, the propshaft housing should be tightly secured to the gear case to prevent relative motion between the propshaft housing and the gear case. Such relative motion causes wear, which leads to increased clearances between the housing and the gear case. Increased clearances permit greater relative motion, and therefore greater wear, which can result in failure of the gear case, the propshaft housing, the propeller shaft, gears, and/or other components. The propshaft housing should also be removable from the gear case to permit repair and/or replacement of internal components.
Known apparatus attempt to at least limit relative axial, rotational, and lateral movement between the propshaft housing and the gear case. For example, one or more threaded fasteners can be used to limit relative axial motion through a clamping action, and the clamping action also limits relative lateral motion. To limit relative lateral movement, one or more o-rings may be located between the outside diameter of the propshaft housing and inside the bore of the gear case to act as shock absorbers. Due to the elasticity of o-rings, relative lateral motion is reduced, but not eliminated.
Another known retention apparatus for securing a propshaft housing to a gear case includes steel tabs that are tightened against the rear face of the propshaft housing, and the ends of the tabs project radially outward from the outside diameter of the propshaft housing into recesses in the gear case bore. The tab thickness is slightly larger than the distance between the face of the propshaft housing and the rear face of the gear case recess, and the tabs bend slightly when fully tightened against the propshaft housing as the front end of the housing contacts a shoulder in the gear case. This bending of the tabs, which is within the elastic limit of the steel, maintains a high axial load on the propshaft housing against the gear case shoulder, which generates enough friction to prevent rotation of the propshaft housing relative to the gear case. The friction between the tabs, the propshaft housing, and gear case recesses does not, however, always prevent relative lateral movement. The ensuing wear tends to loosen the axial clamp load, which then permits relative rotational movement as well.
In other known engines, threads are formed at the propeller end of the gear case, and after locating the propshaft housing within the gear case, a collar is threadedly secured to the gear case and tightly fits against the propshaft housing. The frictional contact between the propshaft housing and the gear case shoulder, and between the propshaft housing and the collar, effectively prevents rotational and lateral movement of the housing relative to the gear case. To prevent loosening of the collar, a thin washer with an outwardly projecting radial tab and an inwardly projecting radial tab is located between the threaded ring and the propshaft housing. The outer tab fits into a slot in the gear case, and the inner tab is folded over into one of the slots on the inside diameter of the threaded collar. Corrosion and marine growth, however, may make removal of the collar extremely difficult, if not impossible, when servicing is required. In addition, the large exposed threads on both the collar and the gear case can be easily damaged and are relatively expensive to manufacture.
In some other known engines, the propshaft housing includes flanges at the housing aft end, and bolts extend through openings in the flanges and engage the gear case, which totally eliminates rotation of the propshaft housing relative to the gear case. The flanges are tightened against the gear case, which securely positions the propshaft housing axially with respect to the gear case. Although securing the propshaft housing to the gear case in this manner effectively eliminates all relative motion between the aft end of the propshaft housing and the gear case, there may be undesirable hydrodynamic consequences of the flange configuration. The propshaft flange arrangement, therefore, is typically only used for low speed applications, i.e., on small horsepower engines.
Another known retention apparatus employs one or more snap rings expanded into a groove or grooves in the gear case bore at the front end of the propshaft housing, and an annular plate is positioned in front of the snap rings. The plate has two or more threaded holes into which screws are tightened after passing through the front face of the propshaft housing. The snap rings are tightly trapped between the plate and the housing. The snap rings provide an axial locating feature, while the friction between the plate, rings, and housing tends to prevent lateral and rotational movement of the housing relative to the gear case. The prevention of relative lateral movement occurs only at the front of the propshaft housing. Lateral movement at the rear end of the propshaft housing is not reduced or eliminated, and excessive wear can progress quite rapidly. Also, the holes in the propshaft housing through which the screws pass must be sealed to prevent leakage of water into the gear case. Sealing the openings can be tedious and time consuming.
The present invention, in one aspect, relates to a propeller shaft housing for being secured in a marine engine gear case bore and configured for being securely engaged to the gear case by threaded screws that pass through bosses in the housing and into threaded holes in the gear case. More specifically, in an exemplary embodiment, the propeller shaft housing includes at least two bosses having holes therethrough, and at least two threaded holes in the gear case are arranged to align with respective holes through the bosses. Respective screws extend through the holes in the bosses of the propeller shaft housing and into threaded engagement with the threaded holes in the gear case.
In the exemplary embodiment, the bosses of the propeller shaft housing are positioned on a same side of a vertical centerline of the gear case, and as the screws are tightened, the screws apply both a forward pressure and a side pressure to the propshaft housing against gear case. The side pressure eliminates movement of propshaft housing in gear case bore. Further, the bosses, screws, and threaded holes in the gear case are positioned on an opposite side of the vertical line as that of the force generated by propeller when in forward gear. As a result, the propshaft housing is tightened to a same side of gear case housing bore as that of the forces generated by propeller in forward gear. Also, the bosses, screws, threads, and propshaft housing are inside the gear case bore. Therefore, no external flow disturbance results from the above described configuration.